Air filtration is used in a wide variety of environments such as automobiles, homes, office buildings, and manufacturing facilities. In many cases, filtration systems are used to remove pollutants such as dust, particulates, microorganisms, and toxins from breathing air, although filtration systems and processes may be used to purify manufacturing environments, process gasses, combustion gasses, and the like.
One particular application of air filtration is in heating, ventilation, and air conditioning (HVAC) systems within buildings. HVAC systems comprise a motor and blower that moves air from a supply through ductwork that distributes the air throughout the building spaces. The air supply may be outside air, recirculated air from inside the building, or a mixture of outside and recirculated air. In these kinds of HVAC systems, air-filtration systems are placed in-line with the ductwork to filter out particulates and organisms that are present within the flow of air.
Another common application of air filtration is in standalone room air-filtration systems. Such a system, which may be portable, is placed in a room to purify the air in an area surrounding the air-filtration system.
Though there are several types of air-filtration technologies such as mechanical filters, frictional electrostatic filters, and electret filters, active electrically enhanced air-filtration systems have become increasingly popular because of their high efficiency. One particular type of electrically enhanced filter includes an upstream screen through which air enters the filter, a pre-charging unit downstream from the upstream screen and upstream from the filter medium, an upstream electrode between the pre-charging unit and the upstream side of the filter medium, and a downstream electrode that is in contact with the downstream side of the filter medium. A high-voltage electric field is applied between the pre-charging unit and the downstream electrode.
Such a filter captures particles via three mechanisms. First, the filter medium physically collects particles in the same manner as a mechanical filter. Second, the high-voltage electric field polarizes particles in the air flow and portions of the filter medium itself, causing the polarized particles to be attracted to polarized portions of the filter medium. Third, the pre-charging unit creates a space-charge region made up of ions within the electric field. The ions cause particles passing through the space-charge region to become electrically charged, and the charged particles are attracted to portions of the polarized filter medium having opposite charge.
Though electrically enhanced filters such as that just described are capable of performing high-efficiency air filtration, the upstream screen in such a design provides little filtration and, therefore, little protection of the downstream filter and electrodes. It is thus apparent that there is a need in the art for an improved electrically enhanced air-filtration apparatus and method.